Mangal Sain

Coverage Study of ATA Signal Strength in India

In this paper, coverage studies of ATA standard time and frequency transmissions on three carrier frequencies 5,10 and 15 MHz have been reported. The theoretically predicted results agree very well with the SINPO reports received from the AIR stations at some typical locations. This is a first coverage report on ATA transmission. The users of standard time and frequency signals in India will find these studies useful.

Some Peculiarities in the Maximum Ionization Density of the F2 Layer

ABSTRACTIn the course of analysis of data on f0F2 at different Indian ionospheric stations on 75°E meridian, two peculiarities have been observed. Firstly, for the equatorial stations showing the bite-out effect, the change in ionization between low and high sunspot activity at the hour of post-noon peak of f0F2 is much higher than the corresponding change at the hour of the pre-noon peak. Such an effect is not observed at middle latitude stations. Secondly, when the variation of f0F2 with sunspot number is considered, the linear relationship which is generally assumed to exist between the two, breaks down at high sun-spot numbers at certain hours of the day. The point at which the departure from linearity takes place depends on the local time and on latitude.These effects appear to be due to abnormal increase in the thickness of the layer during high sunspot activity and meridional transport of ionization away from the equator in the evening hours.

Broadcasting and Standard Time and Frequency Dissemination

All India Radio has been rendering time dissemination service right from its inception and presently it broadcasts time signal pips almost on an hourly basis from 0600 to 2300 hours I.S.T. on medium and shortwave frequencies. In order to improve the accuracy of these time signal pips, Research Department of All India Radio in collaboration with National Physical Laboratory, New Delhi developed a solid state, interface logic unit for use with Caesium Atomic Clock for synchronization of AIR time signal pips.In India, NPL, New Delhi disseminates standard time and frequency information under the call sign ‘ATA’ on 5,10 and 15 MHz frequencies. In order to assess the reception of ATA/NPL transmissions in India, AIR had conducted monitorings of these broadcasts and results were reported. The predicted field strength values have been found to agree fairly well with the observations. However, these investigations were based on very limited monitorings made at a few locations in India. Recently, AIR again conducted...

Study of sudden cosmic noise absorption in relation to corresponding x-ray flares

In this paper an exhaustive study of X-ray flare which occurred on 13 April 1966 between 0706 and 0716 UT has been made. Raw data for this X-ray flare have been converted to the flux energy in erg cm−2 sec−1 and the corresponding time curves have been plotted. N-h profiles for the D-region for χ values of 30°, 50° and 60° have been worked out at the maximum of the flare. N-h profiles for the χ values of 50° and 60° correspond respectively to Manila and Ondrejov.The SCNA data for Manila on 18 Mc/s and for Ondrejov on 29 Mc/s have been employed to work out a model of effective recombination coefficient (αeff).The height of maixmum electron density comes to about 72 km and the corresponding maximum of absorption is found to occur at about 68 km. This is in agreement with the result of Mitra et al. (1966).

Study of X-Ray Flare in Relation to Corresponding Sudden Phase Anomaly

In this paper an exhaustive study of X-ray flare which occurred on 13 April 1966 between 0706 and 0716 UT has been made in relation to the corresponding phase changes observed on three transmission circuits recorded at Inubo (Japan) on NPG (18·6 kc/s), NSS (21·4 kc/s) and GBZ (19·6 kc/s). From these studies the value of Nr/N0 comes to 0·75 where Nr is the electron density at the height of reflection and N0 is the maximum electron density. The height of maximum electron production has been found to be 65 km and the height of reflection at the subsolar point as 58·5 km.Assuming the Chapman layer produced below the D-layer (Chilton et al., 1963), the value of X-ray wavelength responsible for this SPA has been found to be 1·8 A and corresponding flux energy as 1·02 × 10−4 erg cm−2 sec−1.The observed value of flux energy as found at the maximum of X-ray flare on 13 April 1966 comes to 2·1 × 10−4 erg cm−2 sec−1 which is in good agreement with the value calculated from the analysis of corresponding SPA. These re...

Some Studies of Longwave Propagation of Radio Tashkent 164 kc/s

ABSTRACTThe paper deals with some further studies carried out on field intensity recordings of Radio Tashkent on 164 kc/s., made in the Research Department, All India Radio, during the period 1966–67. From the sunset effect on longwave propagation, it has been possible to find the value of α, the recombination coefficient. It has also been possible to find α from various SILs (sudden increase in longwave field intensity) during solar flares at different timings.An attempt has also been made to establish an approximate formula explaining the variations of absorption of longwave signal during the day.

Corpuscular Effects of a Solar Flare as Observed through Sudden Increase in Longwave Field Intensity SIL

ABSTRACTThe paper deals with an analytical study of magnetic storm in relation to the occurrence of SIL. The most probable value of delay between an occurrence of a SIL and that of magnetic storm has been found to be 23 hours. The most probable value of duration of magnetic storm has been found to be 26 hours as against 34 hours found for type 3 flares as observed through SIL.It has been further found that in case of occurrence of class 3 flare as observed through SIL, there is 60 per cent chance of occurrence of magnetic storm as against about 25 per cent in case of optical flares.

A Comparison between Sudden Increase in Longwave Field Intensity (SIL) and Other Geophysical Effects of a Solar Flare

ABSTRACTThe paper deals with an analytical study of time comparisons between various Solar Flare effects such as SIL, SEA, SWF and that of an optical flare. A comparative study of the times of growth and those of decay of the effects has also been made. The most probable value of the time of growth of an optical flare and that of an SCNA is found, to be 5 min. whereas that for an SIL and an SEA is 7 min. The most probable value of time of decay of an optical flare, SIL and SCNA is found to be 14 min. and that of an SEA is 24 min. An attempt has been made to explain these phenomena in terms of relaxation and recombination processes in the ionosphere.

Prediction of Critical Frequency of F2 Layer

ABSTRACTIn this paper we discuss a method for predicting the critical frequency of F2 layer (f0F2). The method makes use of an ionospheric index which is obtained from previous f0F2 data and which is not sensitive to sunspot activity. It is found to be very useful for short time predictions. The results obtained by this method are compared with those obtained on the basis of an assumption of a linear relationship between f0F2 and sunspot number.